4-Way Dac Extension

This extension circuit makes it possible to use a single DAC (digital-analogue converter) for generating four analogue volt- ages. Evidently, the cost of the extension described here is only a fraction of that of four DAC chips. The operation of the 4-way DAC is fairly simple. Assuming that inputsA,BandEofmulti- plexer/demultiplexer IC, are driven low, the output of Al is fed to the + input of A2, while the output of this opamp is con- nected to the - input of Al via the demultiplexer and Ri. C:-:pacitor C2 functions as a storage device. The output volt- age available at terminal 1 UDACbecause Al is dimensioned for unity gain. When the E input is driven high, or when a new code is applied to inputs A-B, the input voltage for A2 is derived from C2, so that the programmed voltage remains available at the output. The function of the other output buffers and capacitors is, of course, similar to that of A2-C2. For optimum performance, C2-Cs should be low leakage capacitors, e.g. mult...